1. Field of the Invention
The invention relates to a belt retractor for a vehicle safety belt.
2. Description of Related Art
Such a belt retractor is known, of example, from EP 1 003 654 B1. The prior art belt retractor has a belt reel onto which the safety belt is wound when the belt strap is reeled in and from which the safety belt can be unwound when the belt strap is pulled out. The belt retractor also has a belt strap-sensitive blocking mechanism which blocks extension of the belt strap when the belt strap is extended with excessive acceleration. The belt strap-sensitive device has an inertial mass which is mounted on the belt reel such that it can be moved against the force of a spring, and a belt strap-sensitive latch which is likewise mounted on the belt reel and which is moved into a blocking position by any movement of the inertial mass caused by excessive acceleration. Such a belt retractor is also known from DE 199 51 791 A1.
Whereas the belt strap-sensitive latch and the inertial mass in these prior art belt retractors are kept away by a spring biasing force from any blocking engagement when the safety belt is wound onto the belt reel, thus allowing the safety belt to be reeled in unimpeded by the belt strap-sensitive blocking mechanism, a belt retractor known from EP 0 273 584 is provided with an additional retarding device which prevents activation of the belt strap-sensitive blocking mechanism when the seat belt is wound onto the belt reel. The disk-shaped retarding device known from the prior art and designed with corresponding engagement recesses for the blocking latch rotates synchronously with the same rotational speed as the belt reel, with the result that the belt strap-sensitive blocking mechanism is rendered inoperable during the entire process of reeling in the belt strap. At the end of the process of reeling in the belt strap, the belt strap-sensitive blocking mechanism is released again for activation.
As the seat belt is reeled in at a relatively high belt reel speed in order to reel in the belt strap as quickly as possible, the belt reel stops rotating abruptly at the end of the process of reeling in the belt strap. This generates the risk of the belt strap-sensitive blocking mechanism being activated and extension of the belt strap being prevented. Sharp tugging on the safety belt when the belt strap is being pulled out in order to put on the safety belt can cause the belt strap-sensitive blocking mechanism to be activated, thus resulting in further extension of the belt strap being blocked. When seat backs in which the safety belt is wholly or partially integrated are folded forwards, this can lead to excessive acceleration of the belt strap extension and thus to activation of the belt strap-sensitive blocking mechanism.